1. Field of the Invention
The invention relates to a control system and control method for an electrical heating catalyzer.
2. Description of Related Art
There is known an electrical heating catalyzer (EHC) as an exhaust emission control device for an internal combustion engine. A known electrical heating catalyzer, for example, includes a catalyst carrier electrically connected to electrodes, a case that accommodates the catalyst carrier and an electrical insulating mat interposed between the catalyst carrier and the case.
In the thus configured electrical heating catalyzer, if an insulation resistance between the catalyst carrier and the case reduces, electricity may flow through the case at the time when the catalyst carrier is energized. Thus, when the insulation resistance of the electrical heating catalyzer has reduced, energization of the electrical heating catalyzer needs to be prohibited.
The insulation resistance between the catalyst carrier and the case reduces not only when the electrical heating catalyzer has a failure but also when condensed water is present between the catalyst carrier and the case or when carbon has adhered to or accumulated on the mat.
Therefore, there has been suggested a technique for, when the insulation resistance between the catalyst carrier and the case has reduced, initially executing the process of removing condensed water or carbon by raising the temperature of the electrical heating catalyzer and then prohibiting energization by determining that the electrical heating catalyzer has a failure when the insulation resistance is small after the process (for example, see Japanese Patent Application Publication No. 2012-072665 (JP 2012-072665 A)).
Incidentally, when condensed water or carbon is removed from the electrical heating catalyzer, energization of the electrical heating catalyzer or raising the exhaust gas temperature is required, so the fuel consumption of an internal combustion engine increases. Particularly, when carbon is removed, it is required to significantly raise the temperature of the electrical heating catalyzer as compared to that when condensed water is removed, so the fuel consumption of the internal combustion engine may further increase.